1. Field of the Invention
The present invention relates generally to reciprocating piston type engines and/or compressors and more specifically to a crank arrangement which permits the stroke of a piston to be selective varied in a manner which varies the displacement or capacity of the device.
2. Description of the Prior Art
In commonly used reciprocating piston engines and compressors each piston is operatively connected with a crankshaft via a connecting rod. In the case of internal combustion engines for example, during the expansion phase, the work done on the piston by the hot expanding combustion gases is transferred to the crankshaft in a manner which induces the rotation thereof.
On the other hand, in the case of compressors, the crankshaft is connected to a source of rotational energy (such as a prime mover or the like) either directly or through a clutch and/or a transmission, and the piston is driven to reciprocate and compress and discharge fluid during the compression phase of the same.
However, in both of these arrangements the connecting rod is connected to the crankshaft via a crankpin the eccentricity of which is fixed with respect to the axis of rotation of the crankshaft. Accordingly, stroke of the piston is not variably adjustable through the crankshaft connection.
This induces the drawbacks that, in internal combustion engines, during low load operation for example, it is necessary to throttle the induction passage of the engine in a manner to limit the output of the engine. This causes the formation of a relatively high vacuum in the induction conduit downstream of the throttle valve and induces the so called pumping loss phenomenon. This, as is well known, deteriorates the efficiency and fuel consumption characteristics of the engine.
On the other hand, in the case of compressors, when it is required to reduce the output it is normally necessary to either apply the rotational power to the crankshaft in an ON/OFF manner (e.g. open and close a clutch) or vary the rotational speed through the use of a change speed transmission. This adds to the cost, weigth and complexity of the system.